The present invention relates to a booster of control type capable of automatically increasing and decreasing an output by electromagnetically operating an atmospheric valve or a vacuum valve.
As an example of a conventional booster of this kind, as disclosed in Japanese Patent Laid-open No. 7-503124 (1995), there is a booster in which a solenoid mechanism is incorporated into a valve body, and a movable member of the solenoid mechanism is shifted by applying electricity to a solenoid of the solenoid mechanism, and a valve mechanism (atmospheric valve or vacuum valve) is opened by the shifting movement of the movable member, independently from the valve operation based on displacement of an input rod cooperating with a brake pedal.
In the booster having the above-mentioned solenoid mechanism, similar to the output in a case where the booster is operated by operating the valve mechanism by the input rod cooperating with the brake pedal, it is desired that the output can also be adjusted within a wide range by the operation of the solenoid mechanism.
However, in the above-mentioned conventional technique, the solenoid mechanism merely controls an opening amount of the valve mechanism on the basis of magnitude of an electric current supplied to the solenoid, but, there is no mutual relationship (proportional relationship) between the magnitude of the electric current supplied to the solenoid mechanism and magnitude of the output of the booster.
Thus, in order to control the output of the booster to desired magnitude by the operation of the solenoid mechanism, for example, as is in an output signal of a master cylinder pressure sensor for detecting pressure of braking liquid outputted from a master cylinder, it is required that a signal corresponding to the output of the booster be fed-back to control the operation of the solenoid mechanism.
To this end, since a sensor for outputting a signal corresponding to the output of the booster such as the master cylinder pressure sensor must be provided additionally, the entire system becomes more expensive.